Method, furnace installation and system for the hot stamping of workpieces

ABSTRACT

A system for the hot stamping of workpieces having a furnace installation, in which workpieces can be heated to a forming temperature, and a forming installation, in which the heated workpieces can undergo forming. A transfer device is provided for transferring workpieces from the furnace installation to the forming installation. The transfer device is arranged in a transfer space, which is delimited at least in certain regions by a housing and largely bridges the space between the furnace installation and the forming installation. Also provided is a method for the hot stamping of workpieces.

The invention relates to a system for the hot stamping of workpieces,having

-   -   a) a furnace installation, in which workpieces can be heated to        a forming temperature;    -   b) a forming installation, in which the heated workpieces can        undergo forming;    -   c) a transfer device, by means of which workpieces can be        transferred from the furnace installation to the forming        installation.

Moreover, the invention relates to a method for hot stamping workpieces,in which

-   -   a) the workpieces are heated to a forming temperature in a        furnace installation;    -   b) the workpieces are formed in a forming installation;    -   c) the workpieces are transferred from the furnace installation        to the forming installation.

Hot stamping has become established especially as a method for hotforming workpieces made of metal to give component parts, particularlyin the automotive industry, and is also familiar under the name presshardening. The workpieces to be formed are heated in a furnaceinstallation, transferred from the furnace installation to a forminginstallation by means of a transfer device, e.g. a multi-axis robot, andare formed there into the desired component part by a pressing tool.

For example, workpieces made of steel sheet are heated to a formingtemperature between about 800° C. and 1100° C. in an “austenitization”process. In practice, the forming temperature for steel sheets made fromconventional boron-manganese-steel alloys is 930° C. Such steel sheetsare often provided with an aluminum-silicon coating (AlSi). Asteel-sheet workpiece of this kind can be a flat steel sheet plate orsheet bar, for example, or even a piece of steel sheet alreadypre-shaped in a previous step, e.g. by cold deep drawing. The heatedworkpiece is then formed and simultaneously chilled in the forminginstallation by means of a cold pressing tool. As a result, themicrostructure of the material changes during the forming process, andthe component parts obtained have a considerably higher strength andstiffness than component parts which are cold-formed from the workpiece.

On the path of the workpieces from the furnace installation to theforming installation, the workpieces generally come into contact withthe surrounding atmosphere and especially with atmospheric oxygen.

However, this can negatively affect the material properties of theworkpieces and hence also the resulting component parts in an unwantedway.

Moreover, the abovementioned workpiece cools down. The extent of thiscooling depends on implementation parameters, such as time, distanceand/or speed, pertaining from the removal of the workpiece from thefurnace installation until forming. However, there can be considerablevariation in the quality of the component parts obtained during hotstamping if different workpieces come into contact with oxygen and areformed at different temperatures.

In order to heat the workpieces to the required forming temperature,various furnace concepts are known. Currently available commerciallythere are, in particular, continuous furnaces, in which the workpiecesare conveyed continuously through a furnace tunnel by means of aconveying system. Common furnaces in this context are roller furnaces,in which the workpieces are conveyed continuously through the furnace ona roller track. There is nowadays also an established practice of usinga plurality of relatively small individual furnaces, in which possiblyonly a single workpiece or at most a small number of workpieces can bebrought to the forming temperature in each case.

It is then the object of the invention to provide a system and a methodof the type stated at the outset which take account of theseconsiderations.

This object is achieved, in the case of a system of the type stated atthe outset, in that

-   -   d) the transfer device is arranged in a transfer space, which is        delimited at least in certain regions by a housing and largely        bridges the space between the furnace installation and the        forming installation.

Thus, according to the invention, a transfer space with a dedicatedhousing is arranged between the furnace installation and the forminginstallation. The atmosphere in this transfer space can differ from thesurrounding atmosphere. In particular, it is possible for an oxygen-freeor at least reduced-oxygen working atmosphere to be present there.Moreover, a largely constant temperature can be maintained in thetransfer space. In this arrangement, the housing does not need to fullydelimit the transfer space. For example, there can be an interspaceremaining between wall elements and the bottom of the system withoutthis having a negative effect on the working atmosphere in the transferspace. The housing can also be formed at least partially by flexiblehousing elements.

It is advantageous if the housing comprises an access, via which one ormore workpieces can be introduced into the transfer space. Theworkpieces then do not pass via the furnace unit, which in this case canoptionally be loaded via an inlet remote from the transfer space, butseparately into the transfer space and can be handled there by thetransfer device.

In this case, it is advantageous if the access is designed as an accesslock, by means of which the atmosphere of the transfer space remainsseparated from the surrounding atmosphere.

It is advantageous if a temperature lock region is formed between thefurnace installation and the transfer device. This avoids a situationwhere the region of the transfer space in which the transfer device ispositioned can heat up to such an extent that the transfer device couldbe damaged. Without such a temperature lock region, too much hot furnaceatmosphere could reach the transfer device each time a workpiece wasremoved from the furnace unit.

The temperature lock region preferably comprises a flow device, by meansof which a fluid flow curtain can be produced in front of the furnaceinstallation.

The housing advantageously comprises an outlet, via which a workpieceremoved from the furnace installation can be transferred to the forminginstallation and which can be closed or opened by means of a gate unit.During transfer to the forming installation, it is not possible to avoida connection between the transfer space and the environment. However, anoutlet having a gate unit enables this connection to be kept to as shorta time as possible in each case during transfer, and therefore a loss ofatmosphere for a change in temperature with effects on the operatingconditions occurs only over the period of time required for the transferof the workpiece to the forming installation.

The transfer device is preferably designed as an articulated-arm robot.This robot is preferably positioned on the ground.

As an alternative, the transfer device can also be designed as asuspended system.

It is advantageous if the volume of the transfer space is as small aspossible. To avoid an unnecessary empty volume, it can be advantageousif one or more filler bodies are accommodated in the transfer space.

The abovementioned object is achieved in the case of a method of thetype stated at the outset by virtue of the fact that

-   -   d) the transfer of the workpieces takes place in a transfer        space, which is delimited at least in certain regions by a        housing and largely bridges the space between the furnace        installation and the forming installation.

The advantages thereby achieved correspond to the advantages explainedabove with reference to the system.

Illustrative embodiments of the invention are explained in greaterdetail below with reference to the drawings, in which:

FIG. 1 shows a side view of a system for the hot stamping of workpieces,having a transfer space, which connects a furnace installation, whichcomprises a separate furnace module for each workpiece, and a forminginstallation;

FIG. 2 shows a view from above of the system in FIG. 1;

FIG. 3 shows a side view of a modified system for the hot stamping ofworkpieces.

In the figures, 2 designates overall a system for hot stamping, in whichworkpieces 4 are formed into component parts 6. The workpieces 4 areworkpieces made of steel sheet, for example, as explained at the outset.

The system 2 comprises a furnace installation 8, in which the workpiecesare heated to a forming temperature. Once a workpiece 4 has reached itsforming temperature, it is removed from the furnace installation 8 withthe aid of a transfer device 10 and transferred to a forminginstallation 12. This comprises, in a manner known per se, a coldpressing tool 14, by means of which the workpiece 4 is formed into thecomponent part 6 and chilled in a forming process. After a predetermineddwell time in the pressing tool 14, in which the component part 6 thenproduced cools to a final temperature, the component part 6 is releasedand removed from the forming installation 12 with the aid of a removaldevice 16 and then fed to its further destination, e.g. a mechanicalfinish machining operation.

It is possible to use multi-axis articulated-arm robots 18 of the kindknown per se for handling workpieces both as a transfer device 10 and asa removal device 16; in the present case, therefore, there is a transferrobot 18 a and a removal robot 18 b.

As can be seen in the figures, the furnace installation 8 comprises aplurality of separate furnace modules 20, each having a dedicated modulehousing 22 delimiting a furnace space 24 illustrated in dashed lines ineach case for one of the furnace modules. In the illustrative embodimentunder consideration, two furnace modules 20 a, 20 b are shown.

The furnace space 24 is accessible from the outside via an opening 26 inthe module housing 22, which can be opened or closed by means of amodule door 28. In the furnace space 24 there is a workpiece carrier(not shown specially), which supports an individual workpiece 4 or aworkpiece group comprising two or more workpieces 4 during heating. Theworkpiece carrier ensures the satisfactory positioning of the workpieceor workpieces 4 relative to the furnace module 20. In particular, theworkpiece carrier can be manufactured from reaction-bondedsilicon-infiltrated silicon carbide.

The furnace modules 20 a, 20 b illustrated are ones in which only asingle workpiece 4 can be heated in each case. This fundamentallyreflects the ideal case but it cannot always be implemented, taking intoaccount the space required for this purpose and the throughput rate ofthe system 2.

If the intention is to heat a workpiece group comprising two or moreworkpieces 4 in a furnace module 20, therefore, the module housing 22 isin each case of correspondingly taller construction and the workpiececarrier provides a plurality of carrier levels. In this case, the modulehousing 22 can have a respective opening 26 at the height of each ofthese carrier levels and can comprise a module door 28 for each of theseopenings 26. As an alternative, it is also possible to move a pluralityof carrier levels up to a single opening 26 in a furnace module 20.

The furnace modules 20 of a system 2 do not have to be of identicalconstruction. It is also possible for there to be different furnacemodules 20, the dimensions of which, in particular the volume of thefurnace space 24 and the cross section of the opening or openings 26,are each matched to different types of workpieces 4 or to a differentnumber of workpieces 4 to be accommodated.

Each furnace module 20 operates independently and, for this purpose,includes at least one dedicated heating device 30. The heating device 30can be an electric heating unit having a heating coil, for example. Asan alternative, IR radiators or gas burners or similar establishedheating technologies can also be considered.

In the case of a modification (not shown specially), a muffle, whichclosely surrounds the workpiece carrier, can additionally be arranged inthe furnace space 24 of a furnace module 20. The muffle can ensureuniform temperature distribution and can protect the furnace space 24and, in said space, particularly components of the heating device 32from impurities such as scale or coating component parts, which can falloff the workpieces 4 in the furnace module 20. It is possible toaccomplish protection of heating components without a muffle by means ofencapsulation of the relevant component parts; with a muffle, this isnot necessary and, as a result, this outlay on construction can beeliminated and it may be possible to reduce costs.

If a protective gas atmosphere is required, the consumption ofprotective gas is reduced since the muffle has a smaller volume than thefurnace space 24. Moreover, the furnace walls do not have to be freedfrom oxygen and water to the same extent as is otherwise customary.

Each furnace module 20 is supplied via a bundle of lines 32 withelectric or fluid operating supplies necessary for operation. Theseinclude especially the supply of energy or fuel to the heating device30, for which purpose the bundle of lines 32 accordingly comprises anelectric lead and/or a fuel line. In special cases, a special furnaceatmosphere, in which the workpieces 4 are heated and which is differentfrom the surrounding atmosphere, can be produced in the furnace modules20. In this case, the bundle of lines 32 also comprises fluid lines, viawhich an atmospheric gas is blown into the furnace space 24 or via whichthe furnace atmosphere can be extracted. The individual lines of thebundle of lines 32 lead to the individual sources of supply, which arenot shown specially here.

A process control system (not shown specially) monitors the correctoperation and the parameters of the individual furnace modules 20. Forthis purpose, each furnace module 20 is fitted with correspondingsensors, which monitor the operating parameters of the furnace module 20and send corresponding output signals to said process control system. Tothis end, the bundle of lines 32 comprises not only the supply linesmentioned but also corresponding data lines.

If a fault occurs in a particular furnace module 20, e.g. if the heatingdevice 30 of a particular furnace module 20 fails, this furnace module20 can be selectively detected. The faulty furnace module 20 can then besegregated from the working process and serviced separately withoutsignificantly affecting the rest of the sequence of the forming processor even leading temporarily to a stoppage of the sequence.

By means of the individual furnace modules 20, it is possible for eachworkpiece 4 to pass through a customized heating process, which can becontrolled separately for each workpiece 4 by means of the processcontrol system.

The furnace modules 20 form a furnace unit 34, which, in modifiedversions that are not shown specially, can also comprise more than twofurnace modules 20 or even just a single furnace module 20.

The transfer device 10, i.e. the transfer robot 18 a in the illustrativeembodiment under consideration, is arranged in a transfer space 36,which largely bridges the space between the furnace installation 8 andthe forming installation 12.

The transfer space 36 is delimited by a housing 38 having housing walls40, wherein the furnace modules 20 project through a housing wall 40into the transfer space 36 in such a way that the openings 26 thereofcan be reached by the transfer device 10. The housing walls 40 arethermally insulated and can optionally be cooled by means of a separatedevice.

The atmosphere prevailing in the transfer space 36 can be different fromthat in the area of the system 2 surrounding the transfer region 36. Ina modified version that is not shown specially, there are furthermoremeans with which a separate working atmosphere can be built up and/ormaintained in the transfer space 36.

In continuous operation, the atmosphere in the transfer space is heatedby the hot workpieces 4 coming from the furnace installation 8 and,where applicable, by the escaping hot furnace atmosphere until a largelyconstant operating temperature is established. If appropriate, atemperature control device can be provided in addition, by means ofwhich a particular operating temperature can be produced and/ormaintained in the transfer space 36.

In the illustrative embodiment under consideration, a temperature lockregion 42 is formed between the furnace installation 8 and the transferdevice 10. For this purpose, a flow device 44 is provided, by means ofwhich a fluid flow curtain 46 can be produced in front of the furnaceunit 8. In practice, an inert gas, e.g. nitrogen, is used as a fluidhere. By means of the fluid flow curtain 46, a temperature barrier isformed between the furnace modules 20 and the transfer device 10. Thisprevents the transfer device 10 from coming into contact with the hotatmosphere of the furnace modules 20, which is released when the moduledoors 28 are opened. By appropriate control of the fluid flow curtain46, negative effects on the workpiece 4, such as, in particular,cooling, are reduced when the workpiece 4 reaches the flow curtain 46.This can be accomplished by changing the direction of flow and/or thespeed of flow, for example.

The housing 38 of the transfer space 36 furthermore comprises an access48, via which workpieces 4 are introduced into the transfer space 36. Inthe illustrative embodiment under consideration, the access 48 comprisesa magazine carrier 50, which can accommodate a plurality of workpieces 4to be processed. In a modified version that is not shown specially,there is also the possibility for just a single workpiece 4 to beintroduced from the outside into the transfer space 36 by the access 48at any one time.

Moreover, the housing 38 comprises an outlet 52, via which a workpiece 4removed from a furnace module 20 can be transferred to the forminginstallation 12. The outlet 52 can be closed or opened by a gate unit54.

As a further illustrative embodiment, FIG. 3 shows a system 2′ in whichcomponents and component parts corresponding to components and componentparts in the system 2 shown in FIGS. 1 and 2 bear the same referencesigns. Here, there is no furnace lock region 42 with a flow device 44.In a modified version that is not shown specially, however, a furnacelock region 42 can be provided in a corresponding manner to that insystem 2.

In contradistinction to system 2, the transfer device 10 is not designedas an articulated-arm robot 18 but as a suspended system 56 with atraversing telescopic arm 58, which can be moved on rails 62 with theaid of a drive 60 and can be pivoted about a vertical axis. The rails 62are arranged on the roof of the transfer space 36. At its lower end, thetelescopic arm 58 carries a gripping unit 64, by means of whichworkpieces 4 can be gripped.

In system 2′, the access 48 is designed as an access lock 66, ensuringthat the atmosphere of the transfer space remains separate there fromthe surrounding atmosphere. A corresponding access lock can also beprovided in the system 2 shown in FIGS. 1 and 2.

To keep the operating volume of the transfer space 36 as small aspossible, filler bodies 68, of which just three filler bodies 68 areshown by way of example in FIG. 1, can be accommodated in the transferspace 36.

Systems 2 and 2′ operate as follows:

Workpieces 4 are introduced into the transfer space 36 through theaccess 48. The transfer device 10 picks up a workpiece 4 from themagazine carrier 50 and puts the workpiece 4 down in a furnace module20. While this workpiece 4 is being brought to its forming temperature,the transfer device 10 loads the second furnace module 20 with anotherworkpiece 4.

Once the first workpiece 4 has reached its forming temperature, thetransfer device 10 removes the workpiece 4 and transfers it through theopened gate unit 54 at the outlet 52 to the forming installation 12,where the workpiece 4 is formed into a component part 6 and is thenconveyed onward by the removal device 16.

During this process, the transfer device 10 picks up another workpiece 4and puts the latter down in the now free furnace module 20. Such a cycleis then repeated, wherein the furnace modules 20 are correspondinglyloaded and emptied in alternation.

In the illustrative embodiments explained above, the furnaceinstallation 8 comprises furnace modules 20 into which the transferrobot 18 a must reach in order to remove a workpiece 4. As analternative, it is also possible to implement a module concept in whichthe workpiece 4 has already been removed from the furnace space 24before the transfer robot 18 a picks up the workpiece 4. This can beachieved by means of a kind of drawer-type solution, for example, inwhich a carrier drawer can be moved out of the furnace space 24 togetherwith the workpiece 4, ensuring that the transfer robot 18 a receivesaccess to the workpiece 4 outside the furnace space 24.

In a modified version that is not shown specially, the furnaceinstallation 8 can also be designed as a continuously operating rollerfurnace of the kind already discussed at the outset.

In the illustrative embodiments explained above, the transfer device 10with all the essential components and component parts is arranged withinthe transfer space 36. In another modified version that is not shownspecially, provision can be made for only the moving components of thetransfer device 10 to be situated in the transfer space 36. In the caseof the transfer robot 18 a, these moving components are, for example,formed by the robot arm, which does not bear a specific reference sign.A functional connection between the component parts outside and insidethe transfer space 36 can be formed through a housing wall 40.

We claim:
 1. A system for the hot stamping of workpieces comprising: a)a furnace installation, in which workpieces can be heated to a formingtemperature; b) a forming installation, in which the workpieces whichhave been heated can undergo forming; c) a transfer device fortransferring workpieces from the furnace installation to the forminginstallation; wherein d) the transfer device is arranged in a transferspace, which is delimited at least in certain regions by a housing andlargely bridges a space between the furnace installation and the forminginstallation.
 2. The system as claimed in claim 1, wherein the housingcomprises an access via which one or more workpieces can be introducedinto the transfer space.
 3. The system as claimed in claim 2, whereinthe access is designed as an access lock, by means of which theatmosphere of the transfer space remains separated from the surroundingatmosphere.
 4. The system as claimed in claim 1, wherein a temperaturelock region is formed between the furnace installation and the transferdevice.
 5. The system as claimed in claim 4, wherein the temperaturelock region comprises a flow device, by means of which a fluid flowcurtain can be produced in front of the furnace installation.
 6. Thesystem as claimed in claim 1, wherein the housing comprises an outlet,via which a workpiece removed from the furnace installation can betransferred to the forming installation and which can be closed oropened by means of a gate unit.
 7. The system as claimed in claim 1,wherein the transfer device is designed as an articulated-arm robot. 8.The system as claimed in claim 1, wherein the transfer device isdesigned as a suspended system.
 9. The system as claimed in claim 1,wherein one or more filler bodies are accommodated in the transferspace.
 10. A method for hot stamping workpieces the method comprisingthe steps of: a) heating the workpieces to a forming temperature in afurnace installation; b) transferring the workpieces from the furnaceinstallation to a forming installation, c) forming the workpieces in theforming installation; wherein d) the transferring of the workpiecestakes place in a transfer space, which is delimited at least in certainregions by a housing and largely bridges a space between the furnaceinstallation and the forming installation.